1. Field of the Invention
The present invention is directed to aqueously dispersed blends of epoxy resins and isocyanate-terminated prepolymers blocked with phenolic blocking agents which may be cured with amines at ambient or elevated temperature to produce coatings, sealants, caulks and elastomers with improved flexibility.
2. Description of the Prior Art
It is known to cure epoxy resins with amines in order to provide high molecular polymers with excellent properties. One of the deficiencies of these polymers is that they do not possess sufficient flexibility for all potential applications. While it is known that polyurethane resins such as isocyanate-terminated prepolymers may be cured with amines to form flexible polymers, blends of these prepolymers and/or epoxy resins with amines are not storage stable and are generally too viscous to use in spray applications.
Reducing the viscosity of these blends with organic solvents is not an acceptable solution because the presence of organic solvents in spray systems is not desirable for environmental reasons. The use of water as a solvent would overcome these difficulties, but the isocyanate-terminated prepolymers are not stable in water. The terminal isocyanate groups react with the water to form amino groups which subsequently react with the dispersed epoxy resin to form fully reacted systems. Blocking the isocyanate groups of the prepolymer with blocking agents would prevent premature reaction of the prepolymers with the epoxy resins, but these systems would not be curable at room temperature because elevated temperatures would be necessary to release the blocking agent.
Accordingly, an object of the present invention is to provide blends of blocked isocyanate-terminated prepolymers with epoxy resins which are storage stable, have an acceptable viscosity for spray applications and can be cured at ambient or elevated temperatures to provide fully reacted coatings, sealants, caulks and elastomers with improved flexibility.
Surprisingly these objects can be achievee in accordance with the present invention as described.
U.S. Pat. Nos. 4,160,065 and 4,190,567 are directed to the production of cationic polyurethane-ureas with terminal amino groups which are subsequently reacted with epoxy resins. U.S. Pat. Nos. 3,931,116 and 3,971,745 are directed to the production of anionic polyurethane-ureas having terminal amino groups which are subsequently chain extended with epoxy resins. U.S. Pat. No. 4,036,906 is directed to solvent-based blends of polyurethane prepolymers with epoxy resins which are subsequently chain extended with polyamines. U.S. Pat. No. 4,403,085 is directed to blends of blocked isocyanate-terminated prepolymers and epoxy resins which are subsequently cured to form films having improved properties. U.S. Pat. No. 4,522,851 is directed to blends of water-dispersible epoxy resins and water-dispersible blocked polyisocyanates which are cured to form coatings with improved impact resistance. Finally, U.S. Pat. No. 4,826,894 is directed to the incorporation of epoxy resins into aqueous polyurethane dispersions in order to improve the humidity resistance of coatings prepared therefrom.